Innovative hybrid device for the simultaneous damping of pressure pulsations and vibrations in positive displacement compressor manifolds

Highligths

• New hybrid device for simultaneous pulsation and vibration damping is presented.

• Waveforms of vibration and pulsation simulations are verified experimentally.

• The methodology for selecting the design parameters of the new device is shown.

Abstract

Manifold vibrations in refrigerating compressor manifolds are the result of pressure pulsations as well as compressor-generated mechanical vibrations. In this article, an analysis of a device combining a TMD (tuned mass damper) and a shaped nozzle for pressure pulsation attenuation is presented. The nozzle shape and geometry is determined on the basis of our previous findings using 3D analysis. The nozzle pulsation attenuation is caused by viscous and vorticity energy dissipation. The nozzle is mounted inside the pipe in the chosen position using springs with tuned stiffness. The nozzle mass and spring stiffness create the TMD. The simulation of the TMD damping using the OpenModelica SimulationX package is presented with kinetic energy transfer from a vibrating pipe to the TMD. It transpired that the result on the pressure pulsations damping of the vibrating nozzle is not as high as it is in the case of a nozzle in a fixed position due to the clearance between the nozzle and the pipe that is necessary in the TMD case. Nevertheless, vibrations are more efficiently damped using the combined TMD and nozzle damping action (28%) than a fixed nozzle (13%). This innovation makes it possible to reduce vibration and pressure pulsation using one device, which is especially important for small refrigerating manifolds, where the size of the damping element is important and vibration reduction leads to noise attenuation. The hybrid suppression device is currently patent pending.

Introduction

Vibrations in volumetric compressor manifolds are one of the most significant problems causing noise and premature piping fatigue (Wachel and Tison, 1994). In small household refrigeration appliances, noise is the most significant issue, while in natural gas pumping stations and compressor installations in underground natural gas storage facilities, excessive vibrations may cause piping failure. The reasons for pipeline vibrations are pressure pulsations and mechanical excitation from vibrating compressors. Low frequencies result from vibrations of the whole machine and high frequencies arise from the operation of the working valves. There are two approaches used to attenuate piping vibrations. The first approach is the tuned mass damper (TMD) where an oscillating mass on springs takes away part of the kinetic energy of pipe vibrations. The second approach is to attenuate pressure pulsations using mufflers or nozzles.

The TMD approach is well known in the literature – the latest experimental work presented in (Lu et al., 2018) deals with an innovative method of optimisation using particle tuning. The theory and experimental validation of a switching and sweeping TMD are presented in (Miani et al., 2018). Designing and tuning of the TMD is presented in (Rana and Soong, 1998; Americano da Costa et al., 2021; Harik and Issa, 2015, Issa, 2014(Harik and Issa, 2015)). The author of (Asami, 2020) presents the application of optimisation method developed for a double-mass TMD to the optimisation of a single mass TMD using transfer functions. In (Ozer and Royston, 2005), the Den Hartog's theory was applied to the multi-degree-of-freedom system. A modified setup of TMD was proposed in (Issa, 2014) where the primary system is attached to the absorber and the latter is attached to the ground.

The latest work on pressure pulsation attenuation using theoretical and experimental approaches for refrigeration compression cycle is presented in (Oh et al., 2019). In (Park et al., 2004), the source identification and frequency response in a compressor suction manifold was analysed using an upgraded approach. Muffler design and attenuation analysis is presented in several papers (Dowling and Peat, 2003; Wu et al., 2018; (Vijayasree and Munjal, 2012)). This is an important issue due to the current frequency inverter-controlled compressor revolutions. Additionally, pressure pulsation are subject to investigation in screw compressors (Wu et al., 2018). The theoretical analysis of pressure pulsations are based on two methods: the real domain time-distance, which is a 1D continuous model; the Helmholtz distributed model in the complex frequency-amplitude domain, which is a distributed parameters 0D method. Friction can be introduced in both models, but in the Helmholtz method, friction is introduced in a distributed form. Methods for pressure pulsation attenuation based on the Helmholtz resonator theory introduce mufflers of different shapes and sizes in the manifold (Vijayasree and Munjal, 2012); Huang and Jiang, 2007). The development of the Helmholtz model is also shown in (Guash et al., 2017; Chassaing et al., 2008). The basic textbook on muffler design, modelling and application is a good source of help in the design process (Munjal, 2014). The extended Helmholtz model is presented in (Cyklis, 2010). The Helmholtz approach to a muffler design is highly efficient for constant revolution speed compressors. In the case of modern variable revolution speed compressors, a Helmholtz resonator designed for a specific frequency have lower efficiency for pulsation attenuation, this is the reason for model extensions (Chassaing et al., 2008).

A properly shaped nozzle application is one of the possibilities for the attenuation of pressure pulsations across a wide range of frequencies. This possibility is shown in several papers (Sadamoto et al., 2004; Lee and Ih, 2008; Min et al., 2014; Ingard, 1970). In the latest approaches for Helmholtz resonators non-linear models have also been introduced (Forner and Polifke, 2017). The basic textbook of compressor manifolds is based mostly on this distributed approach for both vibrations and pulsations (Soedel, 2007). Pulsation mufflers are actually often analysed using computational fluid dynamics (CFD) methods. However the CFD approach is more often applied for car silencers (Zhang et al., 2018) than with compressor manifolds.

The use of a nozzle in a pipeline reduces pressure pulsations on the one hand and causes flow resistance on the other. Therefore, it is necessary to use the optimization of the nozzle size and shape as shown earlier in (Cyklis and Młynarczyk, 2018) (Młynarczyk and Cyklis, 2020). For this purpose, a 3D CFD simulation was used to determine the appropriate nozzle parameters. The detailed methodology of this approach is shown in the above mentioned works.

The above literature analysis indicates that the damping of vibrations and pressure pulsations is an important problem where good solutions are still being sought. The use of a single element combining pulsation damping (nozzle) and vibration damping (TMD element) is a new solution with the potential to reduce vibrations of positive displacement compressor installations.